1. Field of the Invention
The present invention relates to a functional electronic circuit module made by packaging a plurality of electronic parts, including parts generating a large amount of heat (heat-generating parts) and parts having low heat resistance (low-heat-resistive parts).
2. Description of the Prior Art
In recent years, along with the remarkable developments in car electronics, electronic circuits have come to be used in the essential parts of a car, including various automatic control devices and instrument panels. Accordingly, there exists a need for an electronic circuit module which is thin, light, high in packaging density, and excellent in vibration resistance. Since it is necessary to install electronic circuit parts including heat-generating parts and low-heat-resistive parts in a limited space, a high density electronic circuit module must have the electronic circuit parts mounted on a substrate such as a paper phenol substrate, glass epoxy substrate, polyester substrate and composit substrate, which has a conductor on one side or both sides thereof.
A heat-generating part such as a thyristor, power transistor or triode AC switch (TRIAC), is usually provided with a heat radiating fin, through which heat is not sufficiently released. Therefore, it is necessary to provide an allowance of about a 30.degree. C. temperature rise from the atmosphere temperature. On the other hand, a semiconductor part such as an LSI or IC used in a microcomputer is required to have high accuracy and high reliability, generates little heat, and has a maximum operating temperature of about 85.degree. C. If the use of semiconductors in the direct sun in midsummer or in desert is considered, it is necessary to assume that the maximum atmosphere temperature is 80.degree. C. In such a case, there is little room for allowance between the maximum atmosphere temperature and the maximum operating temperature. On the other hand, the electronic circuit module is a high density part in which heat-generating parts and a low-heat-resistive parts are densely packaged without a sufficient distance therebetween. Since any minor malfunction in the electronic circuit module used in the essential parts of vehicles such as automobiles can lead to personal injury, high accuracy and high reliability of such an electronic circuit module are strictly demanded. High accuracy and high reliability are also required with respect to the temperature stress, for example, in starting the engine in cold weather and or to vibration stress while driving on a rough road at high speed.